The present invention relates generally to soundwave probes and more particularly to a soundwave method and device adaptable to measure, for solids, liquids and/or gases, the acoustic characteristic impedance of a medium, the interfaces of vertically-layered materials defining a medium, and the concentration in a medium of a first material mixed in a second material.
It is well known in the art of soundwaves that all materials have an acoustic characteristic impedance which is the product of the density of the material and the acoustic velocity through the material. Known techniques for calculating the acoustic characteristic impedance include separate measurements of the density and velocity. A known method for measuring the velocity, said to be limited to materials such as rubbers and plastics immersed in water, utilizes the reflection of ultrasonic pulses incident normally to a boundary between two media (Filipczynski, L. et al., Ultrasonic Methods of Testing Materials. London, Butterworth's, 1966. p. 83).
Direct measurement of acoustic characteristic impedance has been made in liquid by compensating the damped capacitance of the transmitting transducer with the inductive reactance and measuring the voltage across the transmitting transducer, which will vary with the acoustic impedance at resonance. This known method is limited in dynamic range, and must be in direct contact with the liquid it is measuring. It is more suitable for a laboratory environment.
Also known in the art are ultrasonic transmission liquid level detectors that relay on attenuation and/or velocity between a transmitter and a receiver to locate or control the interface. These devices require direct contact with the vessel contents and can be limited by environmental considerations.
Additionally known in the art are pulse echo methods where the elapsed time from transmission to the reflected signal from the interface determines the location of the interface. These devices also require direct contact with the vessel contents, where environmental conditions as well as interface disturbances can limit their usefulness.
Likewise known in the art is a method for generating lamb waves in a vessel wall and monitoring the received acoustic wave at a separate location. The vessel contents will dampen the lamb waves and from this an interface in the vessel contents can be determined (U.S. Pat. No. 4,118,983, Brazhnikov, 1978). Though this system has none of the drawbacks of systems that must be introduced into direct contact with the vessel contents, the orientation, frequency, wave shape and band pass that must be controlled for the method to work properly make it excessively complex.